In a production process of a semiconductor substrate, in order to perform a liquid treatment by a processing liquid to a surface of a semiconductor wafer (hereinafter merely referred to as “wafer”), a single-substrate-processing apparatus processing a substrate one by one may be used. One of such liquid treatments is an etching treatment which is performed by supplying an etchant to a main surface of the wafer. This single-substrate-processing apparatus comprises a spin chuck rotating the wafer while retaining the wafer generally horizontally, a nozzle for supplying a processing liquid to a center portion of a wafer surface rotated by the spin chuck, and a nozzle moving mechanism moving this nozzle above the wafer.
For example, when it is desired to perform the etching treatment to a device formation surface of the wafer where a device is formed, the wafer is held by the spin chuck with the device formation surface facing upward. Then the etchant is discharged from a processing liquid nozzle to an upper surface of the wafer rotated by the spin chuck, and at the same time, the nozzle moving mechanism moves the processing liquid nozzle. A liquid contact point of the etchant on the upper surface of the wafer moves following the movement of the processing liquid nozzle. The etchant can be spread over a whole area of the upper surface of the wafer by scanning this liquid contact point between a rotation center and a peripheral portion of the upper surface of the wafer. Thus, the etching treatment is performed on the upper surface of the wafer (see Patent Document 1).